The invention relates to a stirring apparatus, intended for sealed mounting on a container filled with material to be stirred. The stirring apparatus has a mounting flange, a stirring shaft bearing a stirring tool and driven at its end (the rearward end) remote from the container, and sealing elements disposed on the side of the mounting flange remote from the container intended for sealing the stirring shaft from the container interior. The distance between the mounting flange and the drive elements of the stirring shaft is bridged by a load-bearing intermediate housing (also called a lantern or cage housing).
In stirring apparatuses disposed on stirring vessels, and where the vessels are overpressure vessels or when the material to be stirred is poisonous, for instance, and must not be allowed to escape from the vessel even in trace amounts, the sealing of the stirring shaft from the interior of the vessel plays a special role. Stuffing-box packings suffice only in very simple cases. More difficult demands have been met by using so-called slide ring seals or mechanical seals. However, in the larger stirring apparatuses these mechanical seals are heavy units which are housed, as a rule, in their own housing. If the stirring shaft has a diameter of 160 mm, for instance, an associated mechanical seal of this kind, together with its housing, weighs about 400 kilograms. Changing such seals when they had become worm out or damaged was accordingly difficult and time-consuming work, which frequently could not be performed by one person working alone. Originally, the gear had to be removed first, as a rule, and the gear drive shaft separated from the stirring shaft; then the stirring apparatus lantern housing had to be removed; next, the mechanical seal had to be lifted either by hand or by removal tools and transported away from the vessel; and finally the mechanical seal had to be driven to a workshop, for instance by fork lift, where the mechanical seal housing could finally be opened and the worn parts of the mechanical seal removed. Thus there was at an early time the desire for simplification and acceleration of the process of exchanging the mechanical seals of stirring apparatuses, if possible performing the operation without disassembling the gear and while the vessel remained filled and the overpressure in the container, if any, was maintained. In order to be able to exchange the mechanical seals which surround the stirring shaft, a space had to be created at some point on the shaft, for instance by opening up split couplings, flange connections or the like, the space being as tall as the mechanical seal housing which was to be removed laterally through this space. In a corresponding manner, this space created after the loosening of the shaft connection and after a portion of the shaft was driven upward also permitted the installation of a new seal.
Because of the necessity first to maintain the tight vessel seal during the operation of changing seals and second to create an interruption in the course of the shaft in order to enable the removal of the seal which was to be changed, the entire structure of the apparatus, and in particular the embodiment of the drive means, which included a gear for stepping down the rpm of an electromotor, had to be considered along with the problems relating to simple exchangeability of the seals.
In stirring apparatuses where the electromotor drive with the associated gear is held at a distance from the vessel above the mechanical seal housing, this distance being established by means of a supporting stand (lantern), wherein at first the gear box was mounted onto the said suporting stand having a lateral window, the applicant first attempted to simplify the creation of the space in the course of the shaft, which was required for removal of the seals, by disposing the gear drive shaft in a bearing which was displaceable upward or outward and by providing this gear drive shaft with an outer thread which could be made to engage a stationary inner thread. This is described in German published application No. 1 782 266. This procedure enabled the axial adjustment of the gear drive shaft by means of the gear drive motor, without precluding the possibility of moving the shaft by hand if exceptional circumstances made this necessary. As a result, the necessity for removing the gear or the gear drive shaft in order to be able to exchange the mechanical seal was already eliminated.
A further proposal of applicant, disclosed in German laid open application No. 1 632 458, then took as its object, by means of one and the same threaded sleeve, which could be driven by a motor, first, lowering the stirring shaft in order to seal the vessel during the changing of the seals and, second, after separating the gear drive shaft from the stirring shaft by means of loosening the coupling connecting the two, driving the gear drive shaft upward, without severing its connection with the gear, so high that the space required for removal and insertion of the seals was created between the ends of the shafts.
The gear box, in both cases, was seated on the supporting housing, called a "lantern" and having a window for the purpose of lateral removal of the seal. The lower portion of the supporting housing also surrounded the actual separate housing for the seal, preferably a mechanical seal.
In order to further simplify the exchange of the mechanical seals in stirring apparatuses, but to save the effort of having to lift up a separate, heavy mechanical seal housing, and in order to embody the entire stirring apparatus in a more compact, space-saving manner, applicant then proposed using the lower portion of the gear housing as the seal housing and placing the unit thus created, in which there was no longer any room intended for exchanging seals or seal elements between the gear housing and the vessel, directly on the vessel, as is disclosed in German Pat. No. 1,750,468. A supporting housing (lantern) with a window intended for the lateral removal of, in this case, only the internal worn parts of the mechanical seal was now placed on the gear housing, but it was now used only for supporting and bearing threaded elements which enabled, in particular, the axial lifting of the gear drive shaft with the internal seal elements. The separation of the gear drive shaft, here embodied as a hollow shaft, from the stirring shaft was effected by removing a tension bolt which was threaded from the top through the hollow shaft and into a conical portion of the stirring shaft.
In order to simplify and accelerate the lateral removal of the seal through the lantern window, which represents one step of the seal exchanging process, and the reintroduction of a new seal by the same way, the seal housing in some cases being very heavy, the applicant further proposed pivotably supporting a carrier element, for bearing the old seal which was to be removed and for the new seal which was to be inserted, on the support stand (lantern) and disposing it so as to pivot about a vertical shaft and to be adjustable in its level on the shaft. This is disclosed in German published application No. 1 809 018.
Finally, for small stirring apparatuses and in particular for vessels which need not remain under pressure during the exchange of the seals and where no separate lifting apparatus is required for the mechanical seal, which in this case is smaller and lighter in weight, applicant developed a more slender and lighter-weight structure. Here, the seal housing itself was embodied as a load-bearing element and the connection point between the gear drive shaft, embodied as a hollow shaft, and the stirring shaft was located inside the unit enclosed by this load-bearing housing. The shaft connection itself was again effected by means of a tension bolt which could be loosened from the top, and the drive motor and the gear formed the top of the apparatus. These latter two elements rested, via two housing portions, on the seal housing embodied as a load-bearing element. The seal housing was intended to be usable in modular fashion in structures having various overall designs. This arrangement is disclosed in German published application No. 20 04 392.
In the structural types described above, the gear had always to be separately adapted to the overall structure; that is, it has to be a specialized gear. In like manner, the threaded elements used for generating axial lifting movements had to be specialized structural components. Both factors resulted in high manufacturing costs. This was also true of the structural type described in German Pat. No. 1,226,987. Here a closed box, called an intermediate housing, was flanged onto the vessel and enclosed the mechanical seal, disposed in a completely separate housing of its own, leaving open a relatively large distancing space. A driving electromotor was flanged onto this intermediate housing at the side. The distancing space was utilized for housing lifting spindles which engaged the base of a gear housing placed on top of the intermediate housing. As is generally known, spindles corrode easily and rapidly seize. A bearing body, here called a lantern, was placed on top of the gear housing and was intended for bearing the gear drive shaft, which extended upward and was embodied as a hollow shaft. The drive shaft was connected to the stirring shaft by means of a clamp connection which could be prestressed hydraulically and held in the stressed state by mechanical means. The housing of the mechanical seal was flanged onto the base of the gear housing. When the motor was uncoupled, the gear housing could be driven upward, together with the housing of the mechanical seal flanged to its base, with the aid of the lifting spindles after the clamp connection between the hollow shaft supported in the gear housing and the stirring shaft was loosened; the extent of this upward movement was such that the housing of the mechanical seal arrived, with the seal, at a point beyond the upper end of the stirring shaft. The patent specification said of the lifting spindles only that a plurality thereof was included in the apparatus and that they were enclosed, via chain gears, by a roller chain, not shown, and by a crank drive, for example, also not shown. It was not discussed whether the crank drive was supposed to be a manual drive means or whether a special motor was to be provided for the spindles; similarly, the guidance of the gear housing was not explained, where, with the mechanical seal housing flanged to its base, the gear housing was to be lifted upward by the spindles beyond the end of the stirring shaft and in the raised position then removed, along with its contents, between the spindles. It was stated in the specification only that "repair operations, such as exchanging the sealing elements" could be undertaken in the raised position. It was described as an advantage in this patent that as result of combining all the structural components needed for sealing, bearing and driving purposes in or on the gear, all the elements necessary from the standpoint of their technical function derived from one and the same delivering factory system and could be tested thereby before installation. In actuality, many different kinds of specialized elements had to be produced by one and the same factory, which is a grave disadvantage in economical terms and one which is associated to a greater or lesser extent with all structural types which have required the use of specialized gears. While on the one hand the structural types intended for rapid and simple exchanging of mechanical seals became increasingly expensive, on the other hand the service life of the mechanical seals became longer, so that it was necessary to perform rapid seal changes only relatively infrequently and in specialized applications. For normal uses, buyers accordingly began to make do without the expensive, rapid-changing apparatuses which they expressly requested for special uses, returning instead to the old, time-consuming procedure of removal of half the stirring apparatus in order to exchange the mechanical seals.
Moreover, many conventionally embodied stirring apparatuses have been in operation for years, which lack any features which simplify the dismantling of mechanical seals or stuffing-box seals. These stirring apparatuses thus present their users with the significant disadvantages noted above whenever the seals must be exchanged, especially the disadvantage of long periods of idleness.